The Firuz Bey Mosque was constructed in 1394 by Mentese governor Firuz Bey, three years after the annexation of the emirate by Ottoman Sultan Bayezid (1360-1403). Inscriptions to the right and left of the mihrab name architect Hasan bin Abdullah and master painter Musa bin Adil.
The mosque is set in a garden precinct that slopes down to the south, bound by madrasa cells to the west. It has a domed, square prayer hall, preceded by a three-room hospice (tabhane) and a five-bay portico to the north. Its minaret rises over the roof with a single balcony.
The portico is surmounted by a barrel vault that rests on six thick piers with pointed arches featuring zigzag molding. Its wider central bay is crowned by an umbrella vault carried on a belt of triangles and is set two steps lower than the side bays, which are level with the ground. Muqarnas carvings adorn the springing of the portico arches. The portico is enclosed at either end by walls pierced with two windows, and the side bays have carved balustrades.
Centered on the portico façade, the mosque portal is richly decorated with polychrome marbles. An archway with joggled red and white voussoirs crowns the doorway, with the carved foundation plaque in its tympanum. The larger arch above the muqarnas portal crown is also carved with floral arabesques and inscriptions, and bears a kufic plaque composed of the Prophet's name. The portal opens into a vestibule that gives access to identical hospice rooms to its east and west, and to the prayer hall to its south. The hospice rooms measure about seven and a half meters per side and have two windows on each of the outer walls, one on top of the other. They are covered by domes raised on octagonal drums with pendentives.
The vestibule opens into the prayer hall with a board arch. Raised two steps above the vestibule, the prayer hall is less than half the width of the hospice and portico at ten meters per side. Its dome is raised on a double octagonal drum with a transitional zone made of muqarnas squinches. The mihrab on the qibla wall is a five-faceted niche flanked by colonettes. The original minbar was moved to an unknown location in Istanbul and replaced with the current marble minbar. The interior is lit with a total of twelve windows, which are arranged in two tiers on the east, west and qibla walls. Four additional windows are pierced into the dome's drum. The mosque is made of blocks of blue-veined marble that give it its popular name, Gök (Sky) Mosque.
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Kiziltan, Ali. Anadolu beyliklerinde cami ve mescitler, 119. Istanbul: Istanbul Teknik Üniversitesi Mimarlik Fakültesi, 1958.